Method of and apparatus for making electrical measurements.



E. L. MCDONALD. METHOD OF AND APPARATUS FOR. MAKI NG ELECTRICALMEASUREMENTS. APPLICATION FILED MAY 8, 1914.

Pafented Dec. s uns.

' 2 SHEETS-SHEET I- E. L. McDONALl METHOD OF AND APPARATUS FOR MAKINGELECTRICAL MEASUREMENTS. APPLICATION FILED MAY 8, 19M.

1,%86,373. I Patented Dec. 3, 1918. W7 2 SHEETS-SHEET 2.

W fig.

l 1 50 9 i I Ilh . ITED STATES PATENT ,OFFICE.

. I nnvair n mcnon'nnn, or SALT LAKE CITY, UTAH.

mnrnon or AND APPARATUS FORMAKING ELECTRICAL MEASUREMENTS.

1,286,373. Specification of Letters Patent. P t t D 3, 1913 Applicationfll'ed May a, 1914. Serial No. 837,317.

To all whom it may concern: 7 the connections for actual operation notbe- Be it known that I, ERVAN L. MoDoN LD, ing shown.

a citizen of the United States, residing at Fig. 3 is a detail plan viewof a contact Salt Lake City, in the county of Salt Lake member showing aportion of a coil with 5 and State of Utah, have invented certain whichsaid member makes contact. A

new and useful Improvements in Methods Fig. 4 shows a side elevation ofthe conof and Apparatus for Making Electrical tact member. I

Measurements, of which the following is a Fig. 5 shows an elevation ofthe inner specification. side of one of the insulating rings of the' 65.10 My invention relates to an improved adcontact member. a R

- justable inductance coil adapted for use in Fig. 6 shows a sideelevation of the rotat making electrical measurements, and for ingconducting ring of the contact member. various other purposes,,inconnection .with Fig. 7 shows a sectional view of the inelectriccircuits connected to alternating'or sulating rings and the conductingring in .15 pulsating electromotive force s. For -ex 7 assembledrelation.

ample, the apparatus is of particular advan- Fig. 8 is an enlargedsectional view showtage in connection with my improved ing the means formaki contact with a method of measuring or comparing electrisingle turnof the coil; andv i cal resistances, capacities, inductance's, and ig. 9is a partial side elevation of the 20 other characteristics ofelectrical circuits, conducting ring showing the means for maka sbriefly-set forth herein, and as moreparing conta ct with a turn of-th'ecoil.

ticularly described in my copending-appli Like numerals refer to likeparts'iand elecation Serial No. 107,706, filed July 5,1916, 'rnents inthe several figures of the drawings, whichis a division of thisapplication..' in which my lnvention is shown as compris- 25 Theprincipal object of this inventionvis ing two electrical conductingcoils 10 and to provide an apparatus comprising an in- 11, which areinductively wound on the ductance coil mounted in fiXedpositionfin samecore. Each coil is made up 'of a plu-' combination 'with a movablecontact a r-. rality of turns which are "insulated from ranged to makecontact with any desired eachother and from the turns of the other 30turn of said coil throughout its-length and coil, the outer coil 11being wound concenthroughout the periphery of the coil. A trically withthe coil 10 and in close proxfurther object is to provide means formakimity thereto. The two coilsfareof equal ing contact with-theinductance coil at any length, preferably made up in sleeve-like desiredpoint between its ends, in combinaform and mounted upon a base plate 12'35 tion with means for accurately determining of insulating material,as shown in Fig. 2. the relative proportionsof thecoil on each TheterminalsllO and 10 of the coil 10 side of the contact point. Stillanother obare connected by means of the electrical ject is to provide animproved contact for conductors 13 to binding posts 14, which makingelectrical connection with a-turn of are permanently fixed on the baseplate 12.

40 the coil throughout the periphery thereof. The terminals 11 and 11 ofthe coil 11 Other objects relate to various features of are connected bymeans of the electrical construction and arrangement which willconductors 15 to the binding posts 16 and 17, appear more fullyhereinafter. v .which are also permanently secured to the Othercharacteristics and advantages-of base plate. A portion of theperipheral sur 45 my invention will be set forth and made apface of thecoil 11 is uninsulated, so that parent in the following specification,of each of the turns of-said coil is. exposed on which the accompanyingdrawings form a the outer periphery thereof, in order that an part. relectrical contact can be made with said In the drawings f I coil at anypoint between its ends. A guide 1 '50 Figure l is a diagrammatic view ofthe rod 18, preferably of rectangular cross secgeneral arrangement andconnections of my tion, is mounted upon the base plate parapparatus,showingthe uniform and symallel to the coils 10 and 11, and has slidablymetrical arrangement of the turns of the mounted thereon a-member 19which carries inductive coils. v I the contact member 20 adapted to makean 65 Fig. 2 is a plan view ofmy apparatus aselectrical connection withthe exposed porsembled in permanent form on a base plate, tions of theturns of the coil 11 at any point between the ends' of said coil. v Agraduated '1 scale 21 is secured to the base plate parallel has fixedthereon the binding and 29. By means of the binding posts 14, the innerinductive coil 10 can be connected in circuit with a galvanometer 30, orother detector of feeble currents.

In order to insure greater accuracy in the adjustment of my apparatus Iprovide a contact member 20 of special form. The outwardly extendingportion of the sliding member 19, which carries the contact member 20,is bifurcated, as shown clearly in Fig. 3, to form two forked arms 39,each of which is provided with an arcuate'flange 39 having an innersurface adapted to conform to a portion of the outer contour of aninsulating ring 40. Each of these insulating rings is concentric withand has an inner diameter slightly greater than the outer diameter ofthe coil 11, and is secured to its corresponding arcuate flange 39 bysuitable screws, or other means of fastening. The inner plane faces ofthe rings 40,,which are then spacedapart, serve as guides or bearings'for a rotatable conducting ring 41,

therewith,

which carries means for making electrical contact with a single turn ofthe coil 11 at any point around the periphery thereof after the slidingmember 19 has been moved to the desired position longitudinally of thecoil. The conducting ring 41 has an inner diameter greater than theinner diameter of the rings 40, and is provided on each side with aconcentric annular flange 41 which is journaled in a correspondingannular groove 40 in the adjacent insulating ring 40. The ring 41 isthus maintained in proper relation to the coil 11, and is prevented fromforming an electrical contact except as hereinafter described. The ring41 is provided at some point on the inner side thereof with a notch 42having an arcuate surface 43, upon which is mounted a spring connector44', whose head 45 is adapted to make contact with the outer surface ofa turn of the coil 11. .As shown in Fig. 8, the head has a surfaceconforming to the contour of the conductor of the coil, so that saidhead will-under the influence of its spring maintain contact with asingle turn of said coil uponrotation of posts 37 28,

the ring 41. The head 45 is also beveled at each side of its contactingsurface so that it will readily slide over successive turns of the coil,as the entire contact member 20 is I moved longitudinally of the coil onthe guide rod 18. Radially outward of the head 45 the ring 41'carries afixedpointer 46,

whose diametrically opposite points 46 project over graduations 4O onthe insulating rings 40, as shown in Fig. 3.

The sliding member 19 carries. a binding post 47, 'to which theconductor 22 leading from the binding post 23 is fastened. The bindingpost 47 is preferably insulated from the member 19, and is provided withan insulated conductor 48, bymeansof which an electrical connection ismade between the conductor 22 and a spring contact 49, which issecured'to, but preferably insulated from, an arm 39 of the member19 andadapted to project into a slot in one of the rlngs 40 to make electricalcontact with the ring 41, as shown at 50. Since the operator of theapparatus moves the contact member longitudinally of the coil 11 bymeans of the sliding member 19, the binding post 47 and associated partsare, preferably insulated therefrom, as stated, in order that saidmember will form no part of the electrical cir-' cuit. 7 The member 19is threadedly engaged by a stud 19*, which may be operated by means of aknurled head 19 to engage the guide rod 18, and thereby secure thecontact member 20 in any desired position longitudinally of the coil 11.I

-'It will be apparent that by means-of a contact member 20, of the formjust described, an electrical connection is made between the conductor22 and a singleturn of the coil 11' at any point-around the'peripherythereof. A ring 40 being properly graduated to indicate the decimalparts of a turn of the coil 11, the operator may from the positions ofthe pointers 20 and 4t determine the number of turns and fractionalparts thereof which are included in each portion of the coil 11 at eachside of the point where an electrical contact is made therewith by thecontact member 20. The rings 40 may he graduated to read in oppositedirections, and two points 46 provided on the fixed pointer 46 so thatthe fractional part of aturn included in each portion of the coil 11 atcorresponding sides of the con tact member 20 may be read directly orthe graduations-may be placed-on the ring 41 and the indicators attachedto the rings 40. In order to facilitate the reading of the po sition ofthe, pointer 46 when it is on the under side of the coil 11, a mirror orother suitable means may be adopted to indicate the reading to theoperator in his position above the coil.

I have above described the parts of my apparatus which I prefer toassemble in permanent form on the base plate or standard, so that theapparatus may be conveniently moved from one position to another to beat alltimes in readiness for operation.. Referring to Fig. l, I haveshown diagrammatically the connections of my apparatus which are usedfor measuring or comparing the resistance of electrical conductors. Thetwo resistances 31 and 32, which are to be compared, are connectedbetween'the respective pairs of binding posts-25 and 16 and 26 and 17,the binding posts 25 and 26 being electrically connected to the commonconnecting plate 27, or to the ground as preferred. The electricalconductors 33, leading from a source of alternating current E.

M. F. or other suitable supply are connected to the binding posts 23 and24. Thus it will be seen that one terminal of the source of electricpressure is connected to the sliding contact member 20.. The otherterminal of this source of pressure is connected to the commonconnecting plate 27, or to the ground, in case the binding posts 25 and26 have been connected to the ground. Heferring to Figs, 1 and 2 it willbe apparent that two parallel electric circuits are formed between thecontact member 20 and the common connecting plate 27 as follows: thecircuit 20, 11, 16. 21, 25, and 27, and the circuit 20, 11 17, 32 26 and27.

It is therefore apparent that-the current entering th coil 11 from thecontact member 20 will at any given instant be flowing in oppositedirections from the contact member in the two portions of the coil ateach side thereof. The inductive action ofone portion of the coil willtherefore be opposed to that of the other portion, so that when thesetwo actions are unequal a current will fiow in the coil 10, in responseto the voltage induced therein, and cause a deflection or indication ofthe galvanometer or other detector 30. Then the inductive action of thetwo portions of the coil 11 on corresponding portions of the coil 10just neutralize each other there will be no flow of current in thecircuit 7 of the coil 10 and no deflection or indication of thegalvanometer or other detector.

Having connected my apparatus as above described, the sliding member19-is adjusted longitudinally of the coil 11 andthe contact member 20manipulated until the inductive effect of one of the above named branchcircuits just balances that of the other branch circuit. In making thisadjustment the contact member 20 is moved longitudinally of the coiluntil a point is reached-w re the detector 30 indicates an approximatebalance. The ring 41 is then adjusted within the insulating rings 40until an exact halance is found. When this point of balance is 11 oneach side of the contact member will just'neutralize each other, withthe result that the voltages induced in the corresponding proportionalparts of coil 10 will neutralize each other. Thus, the point of balancewill be indicated by the galvanometer or detector 30, which will fail toregister when this point in the adjustment has been reached. The scale21 being graduated according to the number of turns in the coil 11, therelative number of turns and fractional parts thereof in the twoportions of said coil at each side of the contact made by the contactmember 20 can readily be determined by reading the indications made bythe pointers 20 and 46 on their corresponding scales. The values of theresistances 31 and 32 will then be directly proportional to the numberof turns in the two portions of the coil 11 at each side of the contactmember, and if one of the resistances 31 or 32 be a known or standardresistance, the value of the other may readily be calculated from theproportion which the number of turns in" the two portions of the coil 11bear to each other, all of which will be readily understood by anyoneskilled in the art to which this invention appertains.

I preferably wind the coils 10 and 11 upon a core of non-magneticmaterial, since I have found that the results following the use of myapparatus are more accurate when an 9.11 core is used than when a coreof magnetic material is employed. The accuracy of the results is alsoincreased by constructing the coils of my apparatus with a relativelylow resistance. The speed with which the apparatus may be used may beaugmented by graduating the scale 21 to read in both directions, andthis also provides a quick and convenient means for checking I haveexplained my invention in connec- 'tion with one particular form andarrangement of'apparatus', but it will be obvious that it may beembodied in other forms ofapparatus which may be operated upon theprinciples which have been set forth herein in connection with theparticular form of apparatus described, and I do not therefore wish 7-to be limited to the particular form and arrangement of apparatusherein described. It will be understood that I contemplate changes inform and arrangement and the substitution of equivalents without departing from the spirit of the invention as defined in the appended claims.

I claim 1. In apparatus of the class described, an.

electrical coil Wound in sleeve form, a guide extending around theperiphery of said coil, and a movable contact element slidably mountedon said guide to contact with said coil at any point around theperiphery thereof.

2. In apparatus of the class described, an electrical coil Wound insleeve form, a guide extending around the periphery of said coil, amovable contact element slidably mounted on said guide to contact Withsaid coil at any point around the periphery thereof, and supportingmeans for said guide adapted to permit movement thereof longitudinallyof said coil. I 3. In apparatus of the class described,- a coil, acontact member movable longitudinally of said coil and arranged tocontact.

with any desired turn thereof at any point around the periphery thereof,said contact member comprising relatively movable members, one of saidmembers having graduations thereon, and a pointer carried by the othermember.

4. In apparatus of the class described, an

electrical coil Wound in sleeve form With the turns thereof insulatedfrpm each other, and a contact member slidably mountedto movelongitudinally of said coil, said contact mem: ber comprising a movablepart adapted to extend around said coil'and to contact With any desiredturn thereof at any point around the periphery cf'thef'coil;

5. In apparatus'of the class described, a coil'vvound in sleeveform andmounted in fixed position, the turns'of said coil being insulated fromeach other but having their outer surfaces uninsulated, a contact member movable longitudinally of said coil, and a guide forsaid contactmember mounted alongside said coil, said contact member comprising apart movable throughout the circumference of said coil to contact Withany desired turn of said coil at any point throughout the peripherythereof.

6. In apparatus of the class described, an electrical conductor Wound insleeve form to form a coil, an annular guide member extending aroundsaid coil, a contact member slidably mounted on said guide member andhaving a part adapted toengage any desired turn cf said coil, asupporting bracket for said guide member, and a member upon which saidguide member is slidably mounted to move longitudinally of said coil.

7. In apparatus of the class described, an electrical conductor Wound insleeve form to form a coil, a pair of annular insulating .menibersextending around said coil, 2. conducting member rotatably mountedbetween said insulating members, a contact element mounted on saidconducting member to engage a turn of saidcoil, means to indicate therelative position of said contacting member With respect to saidinsulating members,

and means to permit bodily movement of said insulating members andsaidconduct ing member longitudinally of said coil.

8.In apparatus of the class described, an

engaged by said flanges, and a contact element resiliently mounted onsaid conducting member and adapted to engage a turn of said coil. v

. 9. In apparatus of the class described, an electrical conductor Woundin sleeve form to form a coil, a guide member mounted parallel tosaid'coil, supporting means slidably mounted on said guide member, apair of annular insulating members carried by said -,,supporting meansand extendin around said coll, an annular conducting member havinglateral flanges, said insulat ing members having annular grooves to be'slidably engaged by said flanges, a contact element resiliently mountedon said conducting member and adapted-to engage a turn 0 s around theperiphery of the turn of'said coil engaged thereby. a

In testimony whereof, I- have subscribed my'name.

, nRvAN L'. MoDONALD. Witnesses R. W. MCDONALD, M. A- SULLIVAN.

aid coil, means to indicate the posi- 1 tion of said supporting meanslongitudi

